Old School Techhttp://oldschooltech.info
Where old school ways meet new technology.Fri, 14 Apr 2017 03:15:37 +0000en-UShourly1https://wordpress.org/?v=4.6.1Heirloom Blueberry Cuttings, Part IV, Monsters!http://oldschooltech.info/2017/04/heirloom-blueberry-cuttings-part-iv-monsters/
http://oldschooltech.info/2017/04/heirloom-blueberry-cuttings-part-iv-monsters/#commentsSat, 08 Apr 2017 16:42:54 +0000http://oldschooltech.info/?p=545As our heirloom blueberry cutting experiment continues (described previously here, here and here), we’ve suffered some losses. As a refresher, our goal is to pack many cuttings together in a means that can be easily separated and replanted later, while at the same time avoiding the use of rooting hormone. Lessons learned to follow.

Here is our planter box three weeks into the experiment (as with most of our photos, click to enlarge):

Looks pretty good, right? Well, our experience with cuttings (including the previous batch a couple of years ago), is that the thinner cuttings seem to do really well to begin with, but then die later on. In comparison, the thicker cuttings seem to take longer to get started, but then are more likely to survive.

My personal tendency is to want to create little bushes in-being out of those scraps, so I always leave more of a plant intact on those little fractal twigs than I should. A branching twiggy thing has more surface area and more budding points compared to the very small cross section for initial nutrient transport or locations for root formation. All that initial growth seems exciting, but this growth is consuming internal energy that you want put into creating roots. Better would be hardly anything visible going on; the plants that did the best a couple of years ago seemed to be the worst for a long time, and then flourished while all the rest died.

True to form, all the little leafing thin twigs you see above have dried up and died. The thicker twigs are hanging in there, with one very large shoot coming from the woody stem to the right.

However, some of the little woody stems seemed to lose their new stalks. We found one perfect little clump of leaves lying in the pan, seemingly otherwise healthy. Unfortunately, monsters have intruded on the experiment. After finding that twig, we noticed that our cats have paid inordinate attention to the planter box. Not seeing any signs of litter boxing, we assumed all was well. Not so. Here is an action shot of Ultimo inspecting the planters:

What the plants see, however, is this:

Sure enough, within moments of the above photo, Ultimo (or Oruchimo in Japanese, roughly translated), performed a kitty full-body rub and twisted the big stalk through about 120 degrees counterclockwise, narrowly missing the nice little clump on the saddle twig to the left. Sadly, that big woody piece was our best performing cutting. It is still hanging in there, but we’ll see.

The same dense pack that made it easy for us to control light and water also made it easy for the plants, as a group, to be attacked by monsters.

Monsters aside, what we have seen in this nearly two month experiment in starting cuttings without growth hormone is no signs of rooting at all on the tiny twigs which have already dried up. Our lessons learned thus far:

• The lack of growth hormone is having a noticeable effect. We’ll see if the lack of this material is an overwhelming obstacle or not.• Many sources say that buds should be removed to encourage root growth. The first batch of cuttings were taken too early for buds to form, but this cutting was almost ready to sprout. The buds were there, but very tiny. We should have removed them.• We kept too much water applied for too long.• We have not maintained a sufficiently acidic soil. Based on a reader’s tip, we’re working on a soil mix with crushed pine bark for the next batch. We’re also working on a better fertilizer mixture to help maintain the right pH for blueberries.• The inability to sprout new little plants from thin-stemmed fractals appears to be confirmed.

We’ll keep this experiment going as long as it will hold out, and see what happens. In the meantime, we’ll be getting the next hormone-free experiment ready, possibly with a control in the mix.

]]>http://oldschooltech.info/2017/04/heirloom-blueberry-cuttings-part-iv-monsters/feed/1Heirloom Blueberry Cuttings, Part III, The Boxhttp://oldschooltech.info/2017/04/heirloom-blueberry-cuttings-part-iii-the-box/
http://oldschooltech.info/2017/04/heirloom-blueberry-cuttings-part-iii-the-box/#respondSat, 01 Apr 2017 16:19:51 +0000http://oldschooltech.info/?p=504In the previous articles in this series, we discussed the background behind our experiment in heirloom blueberry cuttings, and prepared the cuttings themselves. In this article, we expand the series by describing the box and how we used an 18-unit pressed fiber egg carton to house the cuttings. The plastic six quart box is shown below, along with the egg carton nestled inside it:

We like using these pressed fiber egg cartons because they disintegrate so easily when wet. They are practically all wood fiber, with little or no obvious binder or coatings. As with commercial pressed fiber or peat-moss planters, the egg carton gives a great environment to hold water and nutrients while roots are small, and yet allows easy penetration when the roots are larger. Not all paper is suitable for this purpose, however, as many office papers will contain binders, clays, anti-fungal agents and so on which are detrimental to plant growth.

The first step in the process is to remove the cover from the carton, and put it in the plastic box, upside down. This was already done in the previous article to help in the soaking process for the cuttings. We used the cover to help absorb water and keep a humid environment for the cuttings.

Next, we prepare the egg side of the carton by using a shop knife to score the bottoms and sides of each egg cup, as shown below:

The idea here is to give the tiny root hairs somewhere to go and something to grab, rather than keeping them balled up inside the cup until they are much larger and deformed. Not shown in this photo, but important when it is time to repot the cuttings, is to score the interstitial web between the egg cups.We are pretty aggressive about this, cutting down to that molded horizontal line, or farther.

Next, on the other side, we cut three sides of the tower tips and leave the fourth as a hinge, as shown in the closeup below:

The idea here is to put the larger stems through these holes to help them remain vertical in the cups. It isn’t perfect, they’ll still slop to the side a bit, but it is much better than counting on potting soil alone.

Now, it is time for the cuttings themselves. We used the tower tips to hold the longer cuttings, and just dropped the small cuttings into the cups. Try to be careful to put the cuttings in right side up. We’ve done this several times, and still managed to get a couple of them upside down! The raw distribution is shown below:

Next, we spooned in potting soil around the cuttings, straightened each cutting as much as practical, and packed in the soil around them, slightly above the level of the egg cups:

Finally, we then soaked the cuttings and cardboard, again with reverse osmosis water rather than chlorinated tap water, up to the level of the wells remaining after the tower hinges had been cut. This first watering, we are trying to wet the cardboard and the soil, rather than feed the plants. From the perspective of the cuttings, they are still soaking.

For potting soil, we specifically avoided variations called “potting mix” as our experience with these is that they are mostly sand with a lot of fertilizer. We were concerned that the fertilizer would burn the cuttings, so we wanted to control the fertilizer content ourselves. Although the Hyponex still has some fertilizer in it, the amount is small. It also has some random 1″ wood splinters, but these are easy to remove. Had we more time in this area, we would have used our own native compost for this purpose, and would highly recommend that if it is available.

Our philosophy is to avoid over-fertilizing the plants as there are no holes poked in the bottom of the bin. We are intentionally not allowing excess water to drain, and in fact want to keep the soil very wet to allow capillarity to do its job at the cut edges of each plant. As a result, over-fertilizing would result in an accumulating concentration of nutrients, which at some point would dehydrate the cuttings through osmotic pressure. We also don’t want to trigger the plants to grow in excess at this point as they would outrun their ability to feed themselves without roots.

This last point leads to our first failures with this experimental method. As you’ll see in a future post, the most robust plants are the thick cuttings, regardless of length. Most of the very thin cuttings sprouted hard, withered and died. Our experience has been that the early sprouting cuttings don’t do well, while the ones that take their time creating sprouts tend to be the hardiest. It could be that the thin cuttings just don’t have enough exposed channels to support that much activity (although in one case I think we left an air pocket around the cutting base).

In the next post, we’ll talk about fertilizers in more detail, and show some of the progress photos. In future posts, we’ll try a different approach with some thin cuttings and see how that experiment goes.

]]>http://oldschooltech.info/2017/04/heirloom-blueberry-cuttings-part-iii-the-box/feed/0Heirloom Blueberry Cuttings, Part II, The Cuttingshttp://oldschooltech.info/2017/03/heirloom-blueberry-cuttings-part-ii-the-cuttings/
http://oldschooltech.info/2017/03/heirloom-blueberry-cuttings-part-ii-the-cuttings/#respondSat, 25 Mar 2017 13:54:15 +0000http://oldschooltech.info/?p=510In the previous article, we discussed the background behind our experiment in heirloom blueberry cuttings. In this article, we expand the series by describing the cuttings. As you will recall, we accidentally cut a 7-foot shoot from a bush while we were clearing it of vines and saplings back in February. Having had a successful round of cuttings from the same bushes years ago (despite having those cuttings all die later from unrelated neglect), we decided to turn this shoot into cuttings. Only about a foot or two of this shoot had significant bark, the rest being mostly green growth.

Using garden shears, we created three types of cuttings, as shown below:

The first type of cutting was the woody stalk. We didn’t expect this part to do well, and didn’t want to take up space in the cartons with it. But, we didn’t want to throw it out, either. We left this piece about a foot long.

The second type of cutting was the little branchy parts. These would make nice largish plants if we could get them to root. We had a lot of success with this type of cutting previously. These are also about a foot long. In some cases, branches from these were also cut if the overall branch would be too large.

The third type of cutting was about 2-3 inch pieces from the main part of the shoot. We wanted to have at least two bud nubbins (technical term) on each cutting. One of these would be the new live shoots, and the other would help create roots. In practice, we wound up with three nubbins on each small cutting. Since none of these had leaves, there was no need to trim anything else. We did cut off and discard some portions that seemed a little dry.

In all cases, we just cut straight across the shoot. Some sources say to make an angled cut to leave the xylem channels with a larger surface area, but this experimental technique we’re using depends on the cut end sitting more or less flat on the bottom of the rooting chambers.

Next, we soaked all these in our cuttings box. As mentioned in the previous article, this box is a six-quart plastic container (with lid), which we bought from Walmart for about a dollar. We removed the egg carton lid, and placed it upside down in the plastic box. We then test fit all the cuttings into the box. Since we’re going to be soaking them for a while, we wanted all the pieces to fit. You can see below that we had to do a lot of trimming to get everything to fit, so we created many more little cuttings to get the larger pieces down to size:

Once we were satisfied with the fit, we removed all the pieces.

Next, we placed the small cuttings in the bottom of the box on the egg carton lid …

… and then covered them with a half-sheet of paper towel (the kind that is actually absorbent and not just shredded plastic). On top of that paper towel, we layered the larger cuttings:

Next, we put strips of paper towel around the bottom ends of these larger sections:

Finally, we soaked the whole thing with plain water, making sure the egg carton lid was thoroughly saturated:

Ideally, we would like to use rainwater for this, but we used reverse osmosis water instead. In general, for horticulture, we prefer to avoid tap water as the chlorination is more likely to kill the essential microbes.

We kept the cuttings soaking for about a week, mostly covered with the plastic box lid. On sunny days we would place the box outside to help kill fungus, and to heat the box up a bit. Keeping the box warm and humid, like a little greenhouse, helps open the crushed pores at the ends of the cuttings, as well as saturating the cuttings with water to prepare them for the rooting process. You could put a little liquid fertilizer in at this point, but we tend to go very light on fertilizer. At this stage, the goal isn’t to grow the cuttings, just to get them ready for the actual rooting step. We certainly don’t want to encourage rooting during the soaking stage. We also don’t use rooting hormones at any step in this experimental process.

In this article, we’ve described how we prepared the blueberry cuttings for rooting. In the next articles, we’ll talk about the rooting process itself.

]]>http://oldschooltech.info/2017/03/heirloom-blueberry-cuttings-part-ii-the-cuttings/feed/0Heirloom Blueberry Cuttings, Part I, Backgroundhttp://oldschooltech.info/2017/03/heirloom-blueberry-cuttings-part-i-background/
http://oldschooltech.info/2017/03/heirloom-blueberry-cuttings-part-i-background/#commentsSat, 18 Mar 2017 16:39:20 +0000http://oldschooltech.info/?p=501Here at the old school, a dozen or so giant heirloom blueberry bushes line one edge of the property. These bushes produce amazing blueberries each year. We know there are at least two varieties growing here, but we are unsure of the specifics. One variety produces large, plump sweet berries, while the other is a little smaller, but not by much, and produces a sharper blueberry taste. The combination in muffins or waffles is amazing.

Most of the bushes themselves are about six to seven feet high and about as round. Some shoots are as high as eight feet. Fortunately, when the bushes are heavy with berries even these taller shoots are easy to pick.

However, these bushes were neglected over the decades and became overgrown with saw-briars, honeysuckle and various oak and pine trees growing up through them. Numerous dead branches and shoots had been choked off entirely by various vines and were littered among the good. In late 2014, a friend went through the bushes cutting back the dead wood and removing some of the vines and stray oak and pine saplings. She also cut back some of the larger shoots to make the bushes spread better. The scrap from this process was a huge pile of cuttings.

Not wanting to throw all this cutting stock away, we soaked the cuttings in a mixture of water, fertilizer and root stimulator hormone, then placed them in pots and a mixture of potting soil and local soil. We used a variety of planting pot sizes to account for the various sizes of the cuttings. Overwhelmed by the volume of material, we threw much of it away. Properly tended, this discarded material would have made several hundred transplanted cuttings, perhaps as many as a thousand. Unfortunately, we became distracted by other issues and all the cuttings we did process dried up and died in the next two years after a very strong start.

Early in February, 2017, we were again cutting back some of the parasitic vines and tree saplings when we accidentally cut down a seven-foot shoot. We decided to use this shoot as an experiment in a simpler cutting technique that we’ve had percolating since the original labor-intensive process. This technique is entirely experimental for us; you’ll see it unfold live and succeed or fail on its own merits. Rather than the labor-intensive original process, this approach is much simpler and easier to maintain. It also doesn’t use any growth hormones at all, but instead uses a blend of cutting techniques and aquaponics to get to the same end.

The first step was to obtain the egg carton and storage box. We had bought several storage boxes from Walmart months prior for another project, and we also had the pressed fiber egg cartons lying around. It just happened that the egg carton fits nicely inside the storage box, as shown below.

The potting soil we used was Scott’s Hyponex potting soil. What we were looking for is a fine, soft, loamy soil with as little sand as possible, and without big chunks of undigested splinters. The liquid fertilizer was a combination of two Miracle-Gro pourable fertilizers, neither of which contained growth hormones. We’ll get into more details about selecting the soil and the fertilizers in a future article, as well as the potting techniques, progress thus far, and what we could have done better.

]]>http://oldschooltech.info/2017/03/heirloom-blueberry-cuttings-part-i-background/feed/2Double Conversion UPS, Part IIhttp://oldschooltech.info/2017/03/double-conversion-ups-part-ii/
http://oldschooltech.info/2017/03/double-conversion-ups-part-ii/#commentsSat, 04 Mar 2017 15:01:35 +0000http://oldschooltech.info/?p=466In the first article in this series, we described a small double-conversion UPS consisting of a 600 watt AC charger, two deep cycle batteries, and a 1000 watt pure sine wave inverter. In this article, we present test results obtained for a load well above, and a load well below, the applicable 20-amp-hour rating for the batteries. As we will see below, there is a significant difference in the available amp-hours between these two extremes. This result was predicted (along with a description of what the 20-amp-hour rate means), in a previous article on lead acid battery principles.

As a review, our double-conversion UPS system is shown below:

To recap, in the center are our two Duracell 29HM batteries from our ground solar work, purchased from Sam’s Club. Upper right is a 24 volt MicroSolar 1000 watt pure sine wave inverter, also from our ground solar work, and to the left is a 24 volt Samlex Power AC charger, capable of a 25 amp output, or 600 watts. Our regular readers will recall that we had to significantly derate our expectation for available power for the inverter to no more than 700 watts at best, with 300 to 400 watts a typical reliable output. You will recall that the observed quality of the pure sine output of the inverter is exceptional when viewed on the scope (a reader has suggested taking a spectral plot for this and other inverters we’re testing, which we will present in a future article).

We tested this system with a 290 watt load, and then again with a 72 watt load, both tests with the Samlex charger disabled to simulate a power outage. This article presents the results of these tests, and recaps some lessons learned. Both loads were essentially resistive, with some variation over one or two second intervals. There were some inductive load components, but these were negligible.

Both batteries are newish 105 amp-hour (the 20-amp-hour rate, as it is called) deep cycle batteries connected in series, providing nominally 24 volts. This yields a nominal 2520 watt-hour storage capacity if 100% discharged over a twenty hour period. This represents a nominal expected load of 126 watts. So, our 290 watt load is more than twice the nominal load, while the 72 watt load is only a little more than half the nominal load. We’ll see that this difference is significant. You will also recall that our policy is to only discharge the batteries to around 50% of their full capacity. Accordingly, the system should supply a 126 watt load with half the total watt-hours (1260 watt hours) over a ten hour period. Naive math indicates the system should supply a 290 watt load with the same amount of energy in 1260/290 = 4.3 hours, while the 72 watt load should receive this much energy in 1260/72 = 17.5 hours. We call this math naive because it doesn’t account for the different behavior of lead acid batteries under different loads, although it is a good estimate if you have no other data.

In the plot below, we show the voltage and current plotted against time for the 290 watt load.

In previous battery array articles, we’ve set 24.0 volts as our 50% cutoff. Here, we let the test run a little beyond that, down to 23.5 volts, to explore what it means to hit 50% discharge with a current different from the nominal 20-amp-hour rate. Notice the unusual behavior at the start; we threw away the first five minutes of data here to remove surface charge. We didn’t expect to see this unusual behavior last for about thirty minutes. Perhaps a reader can explain this temporary dip, then climb, in the voltage. Our first thought was that this was because of blowing off some deposits on the plates. More later on this topic.

The above 290 watt plot runs for almost five hours, but the voltage passed through the 24.0 volt level, our expected 50% discharge voltage, at about 3 hours and 20 minutes. This is about an hour short of the naive prediction of 4.3 hours, mentioned previously. To see how much energy was being delivered, consider the plot below:

In this plot, the same voltage profile is shown, this time with the percentage of the nominal watt hours on the second axis. When the voltage hit 24.0 volts, only about 37% of the nominal energy had been delivered. By the time 50% of the nominal energy had been delivered, at about four hours and 20 minutes, in line with the naive prediction, the batteries had dropped below 23.7 volts. Clearly, for a load more than twice that of 126 watts corresponding to the 20-amp-hour rate, the batteries have lost about 25% of their energy delivery capacity (37% versus 50%). Effectively, one fourth of our battery array has disappeared under these conditions. This finding is consistent with our previous estimate of a derating to around 70%, which we derived from our hurricane experience and mentioned in the lead-acid principles article. During the post-hurricane power outage, our system used the same batteries and inverter, and operated under a load similar to the 290 watt load during this double-conversion UPS experiment.

Now let’s see what happened with a load much lighter than the nominal 126 watt load. Consider the voltage and current plot below:

In this plot, we see the same initial transient behavior as before. This time, we didn’t throw away the first few minutes. The overall transient lasts about 20-30 minutes here also. You can also see that about halfway in, the load changed to 80 watts. We decided to let the experiment continue as this didn’t seem to be a significant variation for our purposes here.

As mentioned previously, the naive prediction indicated that the batteries would run for about 17.5 hours to produce a 50% discharge at 72 watts (or 15.75 hours for 80 watts). Although we had to terminate the experiment early, after a little under sixteen hours, the batteries had still not reached our arbitrary estimate of 24.0 volts for 50%. At this point, they were still at 24.2 volts. Extrapolating the discharge curve, the batteries would have lasted for a little more than an additional two hours before hitting 24.0 volts, or about eighteen hours total. This is better than the expected 50% discharge, assuming the 24.0 volt level, derived from various manufacturers’ documentation, is actually meaningful.

The real story is shown in the next plot, which shows voltage and percent of nominal energy delivered.

In this plot, regardless of the increased load to 80 watts, we can see the actual delivered energy over time, including the slight increase in delivered energy rate when the load increased. When we terminated the experiment, the batteries had delivered about 48% of the nominal energy. Extrapolating to 50% delivered energy, another 45 minutes would have been required to hit this discharge level. At this point, the batteries would still have been a little above 24.1 volts. Reaching 24.0 volts would have resulted in a delivered power of around 54% of the nominal capacity. This slightly better-than-expected prediction validates the use of 24.0 volts as a rule-of-thumb for 50% delivered energy, assuming that the load is at or below the nominal 126 watt value corresponding to the 20-amp-hour rate.

Interestingly, a significantly lower load does not greatly increase the effective delivered energy capacity of the batteries: a 40% cut in the nominal wattage created only about a 4-5% increase in nominal deliverable capacity. In the other direction, more than doubling the load beyond the nominal created a significant loss, about one quarter of the overall capacity. On average, each 10% load decrease caused an increased capacity by 1%, while each 10% load increase causes a larger loss, about 2%, of the useful energy capacity. Although our sample size is small, I think we can safely predict that a 10% increase from the nominal wattage will result in a 2% decrease in the useful energy capacity, over a reasonable range of variations, with the worst effect being at higher loads. Of course, these measurements were all made under load, rather than allowing the battery to reach a resting voltage, a more significant effect under large loads, but this rule of thumb seems to be an appropriate simplification.

The implication of these results for large arrays is clear. Rather than stressing your batteries by doubling the load beyond the nominal, effectively losing a quarter of your array in the process, investing in more capacity not only adds that new capacity, but recovers the lost quarter as well. In other words, an eight-battery array behaves like eight batteries in a nominal discharge situation at that scale, while a four battery array in the same application acts like only three.

In this article, we’ve seen concrete test data from driving a small-scale double conversion UPS, highlighting actual battery behavior over loads well above and below the nominal discharge rate. We’ve also confirmed 24.0 volts as a reasonable 50% nominal discharge voltage with these batteries, and a predicted capacity variation for different discharge rates (2% loss for a 10% increase in load, 1% gain for a 10% decrease in load, compared to the nominal values). In future articles in this series, we’ll see a larger-scale system in action, as well as see some spectral plots of these inverters and other AC options, including high- and low-end generators.

Update: Reader “The Rat Fink” sends a great description of the voltage transient, aka the “hook”, seen during both experiments:

When placing a load on a good, fully charged Lead-Acid battery, it is normal to see an initial drop in voltage, then rise (under load) … Depending on the load, you should see it drop to 12.0V, 12.1V and then rise up to 12.25V (or so) after about a minute or two. It is what a good battery should do. This is due to mild internal cell warming with current flow in the battery. There are a lot of ways to test the internal resistance of a battery, but most people don’t have the equipment. Anybody can perform this test. I call it “Look for the Hook”. You can see it with a $5.00 meter from Harbor Freight. It is one of the first signs of a bad battery. If you put a load (about 0.25C) on the battery and don’t see the hook (voltage stays on a down-hill slide) that’s a battery on the way out.

]]>http://oldschooltech.info/2017/03/double-conversion-ups-part-ii/feed/1Food Storage Jar Sealshttp://oldschooltech.info/2017/02/food-storage-jar-seals/
http://oldschooltech.info/2017/02/food-storage-jar-seals/#respondSat, 25 Feb 2017 14:14:31 +0000http://oldschooltech.info/?p=442Three decades ago, we bought some glass food storage jars, and really enjoyed them. For the last decade or so, though, they’ve sat in the corner of the kitchen as little more than a decoration because the seals have dried up, cracked and allowed the food to spoil. We recently decided to 3D print some new seals for these.

The first step was to remove the old seals. After plucking off some of the worst portions of the seals, a good amount still remained stuck to the glass, as shown below:

Our first effort to remove this old rubber seal was a disaster. Using a small screwdriver, we tried prying up on the rubber, and managed to bruise the glass. If we had been interested in flint-napping glass, as described in the second chapter of Caveman Chemistry, this would have been great. As it is, the internal cracks rendered the first lid unusable for food. Since we had one jar with existing damage to the lip, we’ve paired these for storing things such as seeds for planting (plus a desiccant pouch to absorb moisture).

The next thing we tried is softening the old rubber first with an orange-based solvent, and let it sit overnight. We used Goo Gone, but many other orange-based options would probably work as well. Rather than using the screwdriver tip to pry, we scraped at the softened rubber as if we were using a tiny glass scraper blade. The first effort removed almost all the rubber. After a second overnight soaking in solvent, the remaining scraps came off completely and easily. The jars and lids then went in the dishwasher for a final cleaning.

Next, we designed a seal in FreeCAD, and used our Taz4 FlexyDually to 3D print a new seal using silver NinjaFlex. Our first effort was a simple flat disc, but this allowed the lid to rub, glass-to-glass, on the jar lip. This is a bad thing. Plus, our first seal was too thick, keeping the wire closure from working properly. Next, we reduced the thickness, and added a small lip to the inner edge, which worked better, but still wasn’t good enough. We then changed to an angled lip, as shown below:

This cross-section is then rotated in space to create the final seal. Note the slight angle on the lip, which works great with the additive process. The first angled lip was too small. The fourth try was what you see above, and is available as an STL file. The final seal is shown below:

Next, we washed the seal, and then installed it on the lid, as shown in the picture below.

The inner diameter of the seal is a little less than the inner glass edge, so the seal is stretched a little bit to get it in place. A side view of the tight seal, and how the lip protects the glass edge once the seal reaches its final orientation, is shown below:

Here we show the lid on the jar:

And a top view:

With this final seal design, there is no scraping of glass-on-glass, and the lid fits snugly on the jar with no stress required to close it. Other than the wire closure showing three decades of age after a trip through the dishwasher, these jars are now as good as new, and catching a second life storing staples.

]]>http://oldschooltech.info/2017/02/food-storage-jar-seals/feed/0Double Conversion UPS, Part Ihttp://oldschooltech.info/2017/02/double-conversion-ups-part-i/
http://oldschooltech.info/2017/02/double-conversion-ups-part-i/#commentsThu, 16 Feb 2017 21:36:03 +0000http://oldschooltech.info/?p=426Most people are familiar with the idea of an Uninterruptible Power Supply (UPS), such as used to help keep a computer running throughout power outages. Intended for only seconds to minutes of use, long enough to get past a short power glitch, or to give the user time to save files and shut down before power fails completely, a home or office UPS is typically small and inexpensive. Plus, a typical UPS will be a square wave or modified sine wave (essentially the same thing with gaps), which is fine for a computer, but we would prefer a pure sine wave output. See our previous ground solar inverter article for more details about these different waveforms.

On the other end of the spectrum, commercial or industrial uninterruptible power supplies will use a huge supercapacitor, plus a backup generator. The idea is that the supercap will supply power for the short time it takes the generator to come online, and then the generator takes the load from there. These systems, intended to keep critical facilities such as hospitals operational, tend to be expensive, and beyond the needs of many people who need more backup power than a small computer UPS, such as to operate a freezer or refrigerator.

Slightly below those very expensive backup systems are alternate energy inverter-charger combinations. Rated into the kilowatts, these systems are also more expensive than what we’ve put together here. By coupling an inexpensive inverter, a small deep-cycle lead-acid battery array, and an inexpensive AC charger, we can create an inexpensive solution. The AC charger keeps the batteries topped off and supplies power while AC is available. Meanwhile, the inverter supplies power to the load from the battery array 24/7, and doesn’t care whether AC power is interrupted. But, if AC power is interrupted, the battery array, as large as you care to make it, can supply the load for hours or days, unlike a computer’s UPS.

An advantage of this system, known as a double conversion UPS, is that if power goes out, the AC charger can be swapped out for a solar charger, a generator, or any other charging source you wish. Planned for ahead of time, switching out charging sources can be seamless and easy; the load will never see the difference. Plus, you have hours to get the work done instead of a mad scramble.

An example of such a system, which we’ve been running for about four months as a longevity test, is shown below:

In the center are our two Duracell 29HM batteries from our ground solar work, purchased from Sam’s Club, and arranged in series as a 24 volt array. Our regular readers may recall that we paid a total of about $200 for both of these batteries.

Upper right is the Microsolar 24v, 1000 W pure sine inverter, also used during our ground solar work (see the bottom of this post for links to those articles), as described in the inverter article from that series. You may recall that this inverter turned out to only be good for about 600 to 700 watts, but has a really nice sine wave output. We paid $189 for this inverter at Amazon, but it looks like it is available for about $30 less at this link. The power that comes out of this system is cleaner than utility power, so we have no concern about using this with inductive loads.

To the left is a new item for this setup, a 24 volt Samlex Power AC charger, capable of a 25 amp output. Coincidentally, this is a 600 watt output, about the same as what the inverter can realistically produce. A closeup of this charger is shown below:

As you can see, this is a no-frills device, with analog meters instead of LED or LCD display. There is a certain charm and sense of robustness about this option. There is another 25 amp Samlex charger in a blue case with no meters for about the same price ($329 as this is written), but we wanted some visible feedback about what was going on with the system. In the above picture, the system is using three amps while running our 70 watt freezer (the white appliance to the right in the first photo).

Tying it all together is 6 AWG THHN cable we purchased from Lowe’s. In this case, we are using all red, with the negatives marked with black electrical tape near the ends. We highly recommend black and red for a more permanent installation. The cables are terminated with 5/16″ crimp lugs, described in detail along with the crimper in this post. Completing the system is a DC breaker, shown to the upper left of the charger in the first photo as a tape-protected mess. This item is a 150-amp automotive Cooper Bussmann CB185-150 breaker which can handle up to 42 volts, perfect for a 24 volt system with above 28 volt charging, and costs around $25. We’ve also evaluated some slightly less expensive alternatives, and they all seem fine.

So, what if AC utility power fails and we have to switch in a solar charger or generator? Simple. Just trip the DC breaker, isolating the charger from the batteries. Then, remove the cabling from the AC charger, route it to a solar charge controller, and reset the breaker. Or, more easily, plug the AC charger directly into a generator’s 110 outlet. The load will continue on the inverter for as long as the batteries last while you get this done.

This kind of system has another nice bonus, particularly when powering sensitive inductive loads. Theoretically, the AC charger, provided it has solid state rectification at the front end, can swallow many low-quality generator outputs that might damage a motor, such as a freezer’s compressor. The pure sine inverter then generates clean power which these appliances require. As a result, this system not only provides continuous operation, it can filter out power glitches from a variety of input sources, including small, inexpensive generators, increasing your backup options.

As mentioned previously, this system has been in continuous 24/7 use for about four months. This week, we decided to kill power and take some measurements. The next article in this series will discuss those measurements, and update our readers on some lessons-learned about battery life and discharge characteristics. We’ll also talk about electronic failure modes and what this means for 24/7 system usage. In future articles we’ll also perform some live swaps to other power sources, and discuss a much larger array that has also been running here for months.

Bottom line, this system, as shown, and its larger cousin, has been performing admirably for these four months, and we are comfortable keeping it in full-time service.

]]>http://oldschooltech.info/2017/02/double-conversion-ups-part-i/feed/3Multicolor Off-Grid Christmas Lightshttp://oldschooltech.info/2016/12/multicolor-off-grid-christmas-lights/
http://oldschooltech.info/2016/12/multicolor-off-grid-christmas-lights/#respondTue, 27 Dec 2016 19:57:02 +0000http://oldschooltech.info/?p=386In previous articles, we have been describing the use of LED Christmas lights as emergency off-grid lighting powered directly from a 24 volt battery array. The first article described using strings of cool white lights. Subsequent articles described building a test fixture for these and warm white lights to overcome problems with untested lights, and then constructing arrays with red LED lights, including the use of an external resistor. In this article, we finish the series by describing the use of multi-color lights, some of which are manufactured with a separate resistor embedded in the string. We’ll also describe a useful design procedure for creating off-grid LED strings using any color combination you wish.

Design Features

You may recall from the previous article that the red LEDs were manufactured as 50-light strings, while the white LEDs were made with only 25-lights per string. All strings tested so far featured many LEDs without integrated resistors, while some LEDs had an integrated resistor to allow the string to be used with varying AC voltage without burning up on the peaks. With one multicolor string, the pattern of the red strings were repeated, with some yellow LEDs having an integrated resistor. However, another multi-color string used separate resistors, which appear as a cylinder inline with the string wiring. Our 150-light multicolor string featured three such resistors, one each for the three 50-unit arrays wired in parallel on this string. We wish to develop a common design procedure that allows lights from any of these various strings to be used with confidence. To develop this procedure, we start by testing the properties of the lights in more detail.

Test Results

Using our test fixture from several articles ago, we tested lights from strings without these external resistors, and lights from a string with series resistors. First, the results without external resistors:

Color

Low/High

Average

Std Dev

Blue

Low

3.06 v

0.06 v

Green

Low

3.11 v

0.08 v

Red

Low

2.08 v

0.04 v

Yellow

Low

2.04 v

0.06 v

Yellow

High

4.04 v

0.02 v

Yellow Orange

Low

2.03 v

0.02 v

As you can see, the yellow LEDs were the only ones which contained an integrated resistor. Unlike the all-red LEDs we tested previously, which contained four integrated resistors per string of 50, only two yellow LEDs per string of 50 contained an integrated resistor. Presumably, this is to make up for the higher voltages used by the blue and green LEDs.

Note also that the LEDs (high-range yellows with internal resistors aside) fall into two main categories: blue and green at around 3.1 volts, and red, yellow and yellow-orange at around 2.0 volts.

Now, the results from the strings with external resistor cylinders:

Color

Average

Std Dev

Blue

2.97 v

0.04 v

Green

2.99 v

0.06 v

Violet

3.05 v

0.05 v

Orange

2.05 v

0.04 v

Red-Orange

2.03 v

0.03 v

Yellow

2.11 v

0.02 v

Since there are external resistors in these strings, none of these LEDs have internal resistors, and so there is no distinction between low and high range. Also, although the averages are a little different than for the previous string, this could just be sampling error.

It is clear that the LEDs still fall into two groups: blue, green and violet at about 3.0 volts, and orange, red-orange and yellow at about 2.0 volts. In the procedure which follows, we’ll call these two groups the blue group and the red group.

The final test we ran was to discover at what voltage each LED starts to produce useful light, and at what voltages the LEDs conduct 5, 10 and 15 milliamps, respectively. To conduct this test, we used a string of four LEDs of similar type, and drove this string through a 220 ohm resistor using a variable lab supply to make the voltage adjustments more controllable. For each data point, we measured the current through the string and the voltage across the string, resistor not included. Then, we calculated the average voltage for the given LED type by dividing by four.

This information from this experiment is summarized in the table below. Cool white and warm white LEDs are also tabulated as a reference. Not shown are the results for the LEDs which came in the strings with the external resistors, but you can expect that the results would be similar for the blue versus red groups. None of the LEDs tested had an internal resistor, as determined by the single-socket test fixture; these can be tested, and our results here confirmed, as a nice homeschool science project.

Color

On

5 mA

10 mA

15 mA

Cool White

2.4 v

2.93 v

3.07 v

3.15 v

Warm White

2.4 v

2.93 v

3.06 v

3.15 v

Blue

2.3 v

2.92 v

3.05 v

3.12 v

Green

2.1 v

3.01 v

3.10 v

3.17 v

Red

1.7 v

1.94 v

2.02 v

2.06 v

Yellow

1.8 v

1.95 v

1.99 v

2.01 v

Yellow-Orange

1.8 v

1.95 v

2.01 v

2.04 v

The green appears to need a little more voltage, but this could be the result of an outlier in the sample set. The On voltage in the table above is highly subjective, and represents the voltage at which the LED appears to be producing the minimal useful light.

Design Procedure

Now that we understand the working voltages of the individual light colors, we can now design our 24 volt strings using a common procedure. We might divide this procedure into two options: one to have more consistent illumination over a wide range of battery voltages at the expense of efficient use of power, and the other to optimize power consumption at the expense of noticeably reduced light at low battery voltages. However, to keep the math simple we’re just going to give a single procedure which gives fairly good results. You may wish to fine-tune your resistor choices with a multi-meter.

We will work through an example of constructing a string which reasonably approximates white light at a distance using multi-color lights, although other combinations will work just as well as far as the procedure is concerned. In all cases, we will try to limit the maximum current to 15 milliamps at the maximum 28.8 volts the batteries might experience. With the LEDs we tested, the blue group gets brighter faster at low currents, so mixing white might need more of the red group to balance out the usual red+green+blue used by computer monitors.

To make our procedure general, we will use a different voltage for each group (blue and red) than our tester produces. Because the tester is a little hot with the red group, and a little cool with the blue group, and the LEDs have a strong non-linear response, we’ll use different voltages for each than those previous tables show.

So, for LEDs in the blue group (blue, green or violet), we’ll use 3.05 volts for our calculations. For LEDs in the red group (red, red-orange, orange, yellow, or yellow-orange), we’ll use 2.00 volts for our calculations. We’ll call these voltages our working voltages. You will note that these working voltages correspond to roughly the 10 milliamp measurement in the previous table.

The first step in the design procedure is to select a number of LEDs using these working voltages to lie somewhere between 24 and 24.5 volts, or perhaps a few tenths of a volt higher if necessary (12 volt designs will halve these voltages, 48 volt designs will double them). Looking at the first table, let’s choose two blue, two green, two red, two yellow-orange and two low range yellow LEDs. This adds up as follows:

Next, calculate the ideal series resistor to limit the current to 10 milliamps at 28.8 volts (12 volt designs will use 14.4 volts here while 48 volt designs will use 57.6 volts):

Resistor = (28.8 volts – 24.2 volts) / 0.010 amps = 460 ohms.

Choose an actual resistor value slightly above this, if possible, although our 10 milliamp design point allows us to choose a value slightly less and still be safe. In this example, we could use any of the following resistors:

• A standard 470 ohm resistor.• The 500 ohm resistor cylinder that came with some light strings.• Two 1000 ohm resistor in parallel for an effective 500 ohm resistor.• Two 220 ohm resistors in series for an effective 440 ohm resistor.

To validate this example, we constructed this string and used a standard 470 ohm resistor in series with our ten LEDs. With this arrangement, the string appears to be producing useful light at 20 to 21 volts, even more so at the normal 24 volt and higher operating range. The actual currents measured at our typical battery array voltages are shown in the table below:

Array
Voltage

Approx
Current

String
Power

Resistor
Power

Resistor
Wastage

24.0

4.6 mA

110 mW

10 mW

9 %

25.0

6.1 mA

153 mW

17 mW

11 %

26.2

8.0 mA

210 mW

30 mW

14 %

28.8

12.5 mA

360 mW

73 mW

20 %

We are satisfied with this result, as it allowed us to design a suitable off-grid LED array more or less blind, without having to tweak the resistor or array elements afterward. And, if we didn’t have the correct resistor, being off a little one way or another is fine. Also, the power wasted by the resistor, while one-fifth of the power at the charging peak, is acceptable at normal operating voltages, and comes nowhere near the 1/4 watt rating of the resistor under any conditions.

In this article series, we have worked through an increasingly scientific process of analyzing inexpensive Christmas LED lights, adapting them as emergency off-grid lighting. Following the design process developed here for any similar LED light in any desired color combination, it should be a simple process to design a useful and long-lived off-grid emergency lighting solution, no inverter required.

]]>http://oldschooltech.info/2016/12/multicolor-off-grid-christmas-lights/feed/0Red Off-Grid Christmas Lightshttp://oldschooltech.info/2016/12/red-off-grid-christmas-lights/
http://oldschooltech.info/2016/12/red-off-grid-christmas-lights/#respondMon, 19 Dec 2016 21:46:23 +0000http://oldschooltech.info/?p=367In two previous articles, we discussed using LED Christmas lights as emergency lighting powered straight from an off-grid battery array, as well as a test fixture to sort individual lights for making a reliable DC-powered string from the random sampling of LEDs in a typical 110 volt string. Both of those articles focused on cool white and warm white LEDs. In this article, we’ll discuss the use of red LED lights. For some applications, red light is a better choice, and a few red strings sprinkled in with cool white strings can even out the spectrum a little bit if warm whites are not available.

First, we removed the red lights from a string, and tested them in our test fixture. For whatever reason, these lights had a slightly different base, and would not easily fit into the fixture we derived from a cool white string. To solve this problem, we pushed the wires a little way out of the socket, as shown to the right. This allowed us to more easily make contact with the red LEDs. As in the previous article, we aren’t trying to precisely measure the LEDs, just group them into low range and high range batches.

Another difference with the red string and either variety of white lights is that the white lights are arranged in strings of 25, while the reds are arranged in strings of 50. This is because red LEDs have a lower forward voltage than white lights (which are actually blue lights with a phosphor coating to make white), so more of them are needed in a string to work with 110 volts AC. While our low-range white lights had a forward voltage of around 3.1 volts, we found that our low-range red LEDs, when placed in our test fixture, had a forward voltage of around 2.0 volts, at a current of around 15 milliamps. The high range red LEDs had a forward voltage of around 4.0 volts, a much wider variation than with the white LEDs.

We also found that in a typical group of 50 lights, there will be only four or five high range LEDs, which makes the overall voltages work out for AC but gets in our way for DC. Because we want to make our strings using ten LEDs, for reasons explained below, four high-range LEDs are too few to efficiently break those up for our 24 volt strings (and certainly too few for those who want to make 12 volt strings).

We may also want to design our strings so that the illumination looks more or less the same whether the batteries are nearing 50% discharge under load (about 24 volts as discussed here) or at the maximum charging voltage of 28.8 volts. Because of this wide variation, we are going to use two designs, both of which use an external resistor to protect the LEDs from accidental over-current. One design will provide more consistent illumination at the expense of about one fourth of the power burned in the resistor, while the other will waste less power but be noticeably brighter at full charge versus reduced charge. In both cases, we want to design for a maximum current of around 15 milliamps. Most LEDs easily handle 20 to 30 milliamps, but we want to give ourselves a little buffer to allow for a longer lifetime.

Even Illumination

Let’s start with the even illumination option. In this case, we’ll use ten low-range LEDs in series. Knowing that our maximum voltage is 28.8 volts, and that in our test fixture the LEDs measure around 2.0 volts while being exposed to 15 milliamps, our ten LEDs will stack up to around 20 volts, leaving the resistor to burn the remaining 8.8 volts. This gives a resistor value of 8.8 volts / .015 amps = 587 ohms. In practice, we’ll use a more convenient standard value of 680 ohms. Although 1/4 watt will be fine, for extra margin this bag of 100 1/2 watt 680 ohm resistors is available from Amazon for under $7, which you can use to create a large number of red LED strings. You can also approximate this with two 100 ohms and one 470 ohm in series if you bought the multiple-value resistor kit, since it does not include a 680 ohm value. Or, we can use three of our 220 ohm resistors in series, for a total of 660 ohms, if you bought a big pack of that single value instead with our previous project. Any of these resistor options work fine.

We can also predict the current when this string is driven at 24 volts. In this condition, we can back off on the LED voltage a little, let’s use 1.9 volts. The string of ten then uses 19 volts, leaving 5 volts to be absorbed by the resistor, or 7 milliamps through the LEDs. This should be acceptable for decent illumination over the entire range.

In practice, we encountered the following performance with this 10-LED string and a 680 ohm resistor:

Array
Voltage

Approx
Current

String
Power

Resistor
Power

Resistor
Wastage

24.0

8 mA

192 mW

43 mW

22 %

25.0

9 mA

225 mW

55 mW

24 %

26.2

11 mA

288 mW

82 mW

28 %

28.8

15 mA

432 mW

153 mW

35 %

At higher voltages, the resistor wastes more of the power used by the string, but this is usually when the off-grid system is flush with available charging power anyway. Note that even worst-case, the string uses less than a half-watt, and usually around a quarter-watt or less. In no case is the 1/4 watt resistor at risk.

Less Wasted Power

For less wasted power in the resistor, we can switch to a 12 low-range red LED string. In theory, at 28.8 volts, 15 milliamps would require a 320 ohm resistor (or the standard 330 ohm value). In practice, a 330 ohm resistor results in about 16.7 milliamps at 28.8 volts. This is remarkably bright on the high end, with reasonable illumination on the low end at 5.8 milliamps:

To chop the peak current down a little, we can switch to a 470 ohm resistor with our 12 red LED string:

Array
Voltage

Approx
Current

String
Power

Resistor
Power

Resistor
Wastage

24.0

4.5 mA

108 mW

10 mW

9 %

25.0

6.0 mA

150 mW

17 mW

11 %

26.2

8.0 mA

210 mW

30 mW

14 %

28.8

12.4 mA

357 mW

72 mW

20 %

In this case, not only is the peak current lower, the overall power consumption is lower, with only a little higher resistor wastage. A bag of 100 1/2 watt 470 ohm resistors is available from Amazon for about $6. Since the highest resistor power mentioned isn’t even close to a quarter watt, a bag of 100 1/4 watt 470 ohm resistors is available for only about $4. Or, the 470 ohm value can be used from the multiple-value resistor kit mentioned previously. Alternatively, two of our favorite 220 ohm resistors can be used in series to similar effect. We’ll be using all these resistor values in future projects, so having plenty around at low cost will be helpful. Remember, each string of ten or twelve red LEDs will need its own resistor.

In this article, we expanded our off-grid Christmas LED lighting project to allow emergency lighting when an inverter is not available. This time, we added an external resistor to the red LEDs, since very few of these are the high-range, current-limiting variety. Although it may seem wasteful to add a series resistor, keep in mind that this is exactly what the high-range lights are doing, only in their case the series resistor is hidden inside the LED substrate. In any case, the power required for each individual string, and the power wasted by the resistor, is still very small compared to the value added by having inexpensive, emergency off-grid lighting available.

]]>http://oldschooltech.info/2016/12/red-off-grid-christmas-lights/feed/0Testing Emergency Solar Christmas Lightshttp://oldschooltech.info/2016/12/testing-emergency-solar-christmas-lights/
http://oldschooltech.info/2016/12/testing-emergency-solar-christmas-lights/#commentsSat, 17 Dec 2016 22:12:27 +0000http://oldschooltech.info/?p=338In a previous article, we described the adaptation of LED Christmas lights as emergency solar lighting powered directly from an off-grid battery array. This approach provides many advantages versus running them from an inverter, including useful lighting while trying to fix your inverter. In that article we made some recommendations about string lengths, current and light levels. Immediately after publishing that article, we discovered that some strings burned out although they should not have, and some strings did not burn out when they should.

To figure out what is really going on, we built a test fixture using materials accessible to most people, and tested batches of cool white, warm white and red LED lights. The results are enlightening, and the whole project makes a great homeschool science lesson. Plus, by using this test fixture with your own lights, you can create light strings, emergency or otherwise, which are more reliable, consistent and long-lasting.

Materials and Tools

The materials shown below were used in this project in addition to the tools listed after.

For convenience, we’ll use 5 volt USB power for our test fixture. You can use any USB charging source for this fixture. However, there is something poetic about using a cigarette lighter adapter, attached to our off-grid 24 volt array, to power our test fixture to characterize what will become our 24 volt light strings.

Before assembly, homeschoolers may wish to use an ohmmeter to verify the resistor value and discuss the color codes. The resistor we used is actually a 219 ohm resistor, which is well within the 5% tolerance. This value will be useful in a science project spreadsheet, mentioned later.

Assembly

Our materials are to be assembled to create the following circuit:

Note that the socket has a little tab on it, both in the diagram and in real life. This tabbed side represents the anode, or positive side of the light, and is attached to the red lead wire in our fixture. For the resistor, we are using the same resistor value as in our field phone Morse decoder project, so if you have to buy some (noted later) you can use the same value on both projects.

The first step is to prepare the USB cable. We started with an old USB A-B cable, the kind with the chunky home-plate shaped end that almost nothing uses anymore but always seems to be the first one you find when looking for a mini- or micro-USB cable. Almost everyone has one of these lying around unused, or knows someone who does. Cut about two feet from the flat end, the A side that goes into the computer or charger adapter. Then, strip about two inches of the outer insulation and peel back the shield and inner foil wrapper. The cable will now look as shown below:

You will notice four wires, shown here as red, black, white and green. Red and black carry the five volts that we’ll use in our tester. Now, carefully and neatly trim all the shield wire back, as well as all the foil. Then, trim off the green and white wires to unequal lengths to prevent them from shorting against each other, the red or black wires, or the shield wires or foil. In the photo below, we have also stripped the ends of the red and black wires and tinned them with solder:

Next, make all the connections as shown in the previous diagram, soldering where indicated with the dark circles. The finished assembly is shown below:

The USB connector supplies power, the red and black plugs attach to the voltage and common terminals of a voltmeter, respectively, and the socket accepts the LED being tested. The resistor and most of the connections are hidden beneath heat-shrink tubing. Underneath that outer heat-shrink is more, smaller heat-shrink tubing around the individual connections. The main job of that blob on the end, and the long wires for the meter, USB and LED socket, is to keep mechanical stress off of the resistor. You can accomplish the same goal by hot-melt gluing that end of the assembly to some rigid stick, like an ice-cream stick or a KNEX. Even if the LED socket is directly shorted, the resistor can never experience more than an eighth of a watt, so we don’t have to worry about thermal stress either.

As noted in the diagram, all the black wires from each cable are connected together in the blob at the end. The USB red wire is connected to one end of the resistor, and the other two reds are connected at the other end of the resistor. Make sure that these three connections don’t short against each other, and it will work fine.

Finally, the ends of the meter wires are inserted into the holes of the solderless banana plugs, and the screws tightened. Whether stackable plugs, as used here, or the more widely available and less-expensive straight-through kind are used, is unimportant. We have tinned the ends of the stranded lead wires first to give the plug screws something to bite into.

Using The Test Fixture

To use the test fixture, prepare it by plugging the banana jacks into a voltmeter, or a multi-meter set to measure DC voltage. Plug the USB connector into a USB charging source. We used a SoftBaugh USB charging adapter, attached to a NOCO GC017 cigarette lighter adapter with battery clamps, and then to our 24 volt battery array. Homeschoolers will wish to measure and record the open-circuit voltage which results for later use in a spreadsheet for the project. In our case, this was 5.23 volts. USB charging voltage is allowed to vary between 4.75 to 5.25 volts. Although most chargers will be on the upper end of this range, it is important to check. This voltage, along with the resistor value, will affect the results you measure with your test fixture.

Next, remove bulbs from their original sockets. This is easily done by first lifting the tab, and then inserting a thin, flat-bladed screwdriver in the gap between the socket and the LED housing. Twist slightly and the housing will jack out of the socket, making it easy to remove. It is then a simple matter to press the LED housing into the test socket, keeping the tabs aligned, until the LED lights. Record the voltage which results.

Note that it is not necessary to seat the housing all the way into the socket. Just making contact is enough. Also, some of the LEDs, especially on the white strings, will be backwards in the sockets. These units came from half of the three-wire bridge sockets. By putting these LEDs in backwards, the manufacturer could simplify inventory. If desired for these 1-in-25 LEDs, pull the candle-shaped clear plastic shield off, remove the LED, flip it around and put it all back together again. You may need to trim the leads, and you will probably break the leads. It may not be worth the effort to salvage these units.

Experimental Results

Some LED varieties fall into two ranges, a lower voltage representing no internal resistor, and a higher voltage representing a built-in resistor. Other varieties appear to have a consistently small embedded resistor. We tested cool white, warm white and red LED Christmas lights, and discovered the following mix of test voltages among the white varieties. Red and other multicolor LEDs have different behavior, and will be addressed in a future article.

LED Type

# Per
String

Low Range
Voltage

Low Range
Occurrence

High Range
Voltage

High Range
Occurrence

Cool White

25

3.2 (+/- .1)

3 in 4

4.2 (+/- .1)

1 in 4

Warm White

25

3.1 (+/- .1)

2 in 3

4.1 (+/- .1)

1 in 3

As shown above, both white LEDs had a large group centered around a low voltage, indicating little or no internal resistance, and a smaller group centered around a higher voltage, indicating a moderate internal resistance. The warm white LEDs were approximately one-tenth of a volt lower than their cool white counterparts. The warm white LEDs also contained more high range units, 1 in 3 versus 1 in 4 for cool white, probably to make up for the lower average voltage. For both white styles, each string of 50 units was actually configured as two 25-unit strings in parallel.

These results confirm online reviews which claim that one in four strings is dead-on-arrival, or fail almost immediately after their first use. We suspect that the manufacturer creates a blend of no-resistor and high-resistor units in the above proportions, and then relies on probability to insert more or less the correct proportion in each string. Sometimes, however, the tails of the curve strike, and strings are either too dim or burn out quickly, depending on how many high-range resistor units have been used in that particular string.

We also analyzed our four-string and six-string that both used about 11 milliamps, as noted in that previous article. The six-string had three each of high- and low-range LEDs, while the four-string was all high-range LEDs. These strings were cut from the larger string at random, and just happened to work out correctly, which further supports the hypothesis that the manufacturing process is random rather than a predetermined pattern. Additional sampling shows no discernible pattern on fresh strings.

A homeschool science project may wish to record the exact values encountered from a variety of strings, plot these, and analyze.

Recommended Strings

Based on these results, we now recommend constructing the following off-grid emergency lighting strings for 24 volt arrays. We’re recommending a variety here, to account for the more or less random mix of LEDs you might encounter. Because of granularity, 12 volt options are limited (half of the 4+2 options), but 48 volt users can simply double the numbers shown.

LED Type

# Per
String

# Low
Range

# High
Range

Nominal
Current

Remarks

Cool White

6

3

3

9 mA

Long Life

Cool White

7

5

2

7 mA

Long Life

Cool White

6

4

2

11 mA

Brighter

Warm White

6

3

3

11 mA

Long Life

Warm White

7

5

2

10 mA

Long Life

Warm White

6

4

2

15 mA

Brighter

It is not necessary to sort or cull beyond identifying which range a particular LED occupies. The variations within each range are small enough to be ignored. Although warm white uses a little more current, we recommend those over the cool white as the light quality is better. Even the 15 mA option uses less than a half-watt.

Sources For Materials

While we plundered our sponsor SoftBaugh’s R&D stock for materials, readers may wish to purchase components from the following sources:

• Resistors can be purchased in five-packs locally from RadioShack for about $1.49, or you can get a pack of 50 from Amazon for about that same price. Don’t worry about having that many extra lying around, these things are always handy to have in various values. Even better would be a kit with 25 each of 16 popular values for around $10 from Amazon. That kit contains values that are also useful for long, custom wiring with the field phone remote bundles.

• Banana plugs can also be purchased locally from Radio Shack for between $3 and $10 for a red and black pair. The least expensive you can find will be fine, but we prefer the solderless set-screw variety as these are easier to reuse among projects. The fancy side-entry Pomonas used in this project were overkill. Or, you can get a set of 20, ten each red and black, straight-through plugs from Amazon here for about $8. As with resistors, having more of these lying around is a good thing.

• We used a SoftBaugh charger adapter, as noted above, but any will be fine, or for that matter, any charging source. Just to be safe, we recommend a source that is not your PC, and even the weakest charging adapter will be fine for this project, which, worst case, uses a maximum of 25 milliamps.

Conclusion

In this article we discussed building a tester for Christmas LED lights so that they can be used for reliable off-grid emergency lighting, powered directly from a battery array. In a future article in this series we will use this same tester to analyze the non-white varieties, as well as construct longer strands of more easily employed lights.